Nuclear reactant drugs such as bifunctional alkylating agents or nitrosoureas have the potential to interact with and modify chromatin constituents. It is proposed that differences in nuclear architecture between different cell types may influence both the qualitative and quantitative interaction of these drugs and the potential for cellular repair of drug-induced lesions. Our preliminary investigations have shown that a strain of rat carcinoma cells (Walker 256) resistant to conventional alkylating agents demonstrated no cross resistance to nitrosoureas at equivalent drug concentrations. The basis of our proposal is to determine how the molecular pharmacology of nitrosoureas causes cytotoxicity where alkylating agents do not. Resistant and sensitive Walker cells (both in culture and in vivo in rats) will be treated with two representative radiolabelled alkylating agents 32p-cyclophosphamide 35S-sulphur mustard or two nitrosoureas, 2-(3-(2-chloroethyl-14C)-3-nitrosoureido)-D-glucopyranose (chlorozotocin) or 1-(2-cloroethyl-14C)-3-cyclohexyl-1-nitrosourea (CCNU). For carbamoylation studies CCNU will be labelled in the cyclohexyl ring. Drug effects upon the following molecular events will be considered: (1) Morphological and biochemical properties of the plasma and nuclear membranes. (2) Possible differential alkylation of chromatin in functionally (replicative, transcriptional) or structurally (sub-nucleosomal) distinct domains of the nucleus. (3) Differential repair of such lesions. (4) The importance of carbamoylation (vs alkylation) of structural and functional nuclear proteins. (5) Differences in acetylation, methylation and ADP-ribosylation of nuclear proteins which may alter the nuclear processes of transcription, chromatin condensation and repair. (6) The influence of steroid-induced nuclear events on drug interactions with chromatin. Potential differences between the resistant and sensitive cells will be pursued with a view to determine their relevance to drug resistance/sensitivity.